A better understanding of the pathogenesis of inflammatory acne is essential for formulating new concepts for improved therapy. Our current research has involved the microbiological and biochemical analysis of isolated pilosebaceous follicles from skin of subjects with acne compared to acne free controls. Such studies have defined the physiologic quantities of the different kinds of bacteria, and lipids within these microscopic structures. Experiments using such physologic quantities in turn has led us to question the validity of the fatty acid theory in explaining the role of P. acnes in the pathogenesis of inflammatory acne. Thus our present proposal is for a reevaluation of the role of P. acnes in acne and for analysis of the comparative inflammatory effect of the different intrafollicular components. In addition, the finding that P. acnes (synonymous with C. parvum) is a powerful immunopotentiating agent in man and animals, has led us to re-evaluate the possibility that immunologic factors may be of significance in the development of severe nodulo-cystic acne. We propose to analyse the immunologic status of patients with severe modulo-cystic acne for general immunologic competence as well as for specific immunologic reactivity to P. acnes.